Can and where can I update Line 16 on Form 1040X?

[Critter-3]

The program assumes you made the entire payment on the original return.   If you did not then you will need to print the return and make the change manually and complete the rest of the lines on the 1040X then ink sign and mail in the return.   

If you use the downloaded version you can switch to the FORMS mode and make the change as an override but you will have to mail in the amended return as well.  

[xmasbaby0]

Do you mean you already filed a Form 1040X but the amount you put on line 16 is wrong?   You cannot "update" it while it is still being processed.   Sorry.   Sending in another amended return while they are processing the one already sent would just cause confusion and more delays.   If you made a mistake on line 16, the IRS might catch it and fix it for you.   Otherwise you are going to have to wait.  Do not send in another return now.   You are already in for a long wait for them to process your amended return---don't make it worse.

Even during “normal” times it takes about four months for the IRS to process an amended return.  During the pandemic and due to the severe backlog at the IRS it is taking much longer—six months or more for many amended returns.  Do not expect quick results from amending.  When the IRS issues a refund for an amended return it will be by check.  They do not make direct deposits for refunds for amended returns.  You can watch for information here:

https://www.irs.gov/Filing/Individuals/Amended-Returns-(Form-1040-X)/Wheres-My-Amended-Return-1